Vibrating screen



June 26, 1923. 3,459,843

B. A. MITCHELL VIBRATING SCREEN Original Filed July 7, 1919 3 Sheets-Sheet 1 1919 3 Sheets-Sheet 2 B. A. MITCHELL VIBRATING S GREEN Originalv Filed July '7.

June 26, 1923 June 26, 1923.

B. A. MITCHELL VIBRATING SCREEN 3 Sheets-Sheet 5 Original Filed July '7, 1919 Mia 26M M M w wk M - Patented June 2%, 1%23.

barren stares BENJAMIN a. rarronnrm, or sr. e-noaen, nnw roan.

VIBRATING- SCREEIG'.

Application filed July 7, 1919, Serial No. 308,922. Renewed April 19, 1923.

T all whom it may concern.

Be it known that I, BENJAMIN A. MITCHELL, a citizen of the United States, residing at St. George, Staten Island, in the county and State of New York, have invented certain new and useful Improvements in Vibrating Screens, of which the followin" is a specification.

This invention relates to new and useful improvements in vibrating screens, and the form of the invention herein. described is a modification of the inventions covered by various applications heretofore filed by me.

The principal object of the invention is to provide an improved screening apparatus embodying means for vibrating and distorting the meshes of a woven Wire screen in order to dislodge the particles which tend to clog the screening medium. A. further object of the invention is the provision of improved means for mounting the vibrator and the screening medium in order to bring about in the screening medium vibrations of the desired character. @ther objects relate to various features of construction, arrangement and operation which will appear more fully hereinafter.

The nature of the invention will be understood from the following specification, taken with the accompanying drawings, in which one embodiment is illustrated.

In the drawings-- lfiigure 1 shows a vertical section through the charging and receiving hoppers of a screening apparatus, showing my improved vibrating screen in side elevation;

Fig. 2 is a longitudinal sectional view on the line 2-2 of Fig. 1;

Fig. 3 is a longitudinal sectional view through the rotary vibrator on the line 3--3 of Fig. 1;

Fig. l is a transverse sectional view on the line 4:4 of Fig. 1;

Fig. 5 is an enlarged sectional view taken normally to the screening medium transversely to the axis of the vibrator, showing diagrammatically the character of the vibrations set up in the screen; and

Fig. 6 is an enlarged plan view of a portion of the screen, showing the distortion of the meshes.

The invention comprises a supporting frame 10 which is provided at its upper end with an arm 11 pivotally connected to a bracket 12 carried by a supporting member 13. This frame'comprises a lower arm 14,

which is threadedly engaged by a bolt 15 adapted to rest at its lower end upon the abutment 16. The bolt 15 maybe adjusted and locked in adjusted position by the nut 17 in order to regulate the inclination of the frame 10 and the screening apparatus carried thereby. The frame 10 also comprises upwardly extendin curved arms 18 which are formed integrally with the face of the frame and adapted to'support the screen partially, as hereinafter described.

Mounted upon th body portion of the frame between the arms 18 is a vibrator casing 20 which is secured to the frame by a strap 21 and bolts 22. The casing 20 is provided with oppositely extending cylindrical portions 20, each of which has rigidly secured thereto a supporting plate 24. These plates are provided with apertures to engage the tapered ends of the casing and are secured in position b keys or the like. The upper edges of the p ates 24 lie in one plane preferably parallel to the body portion of the frame 10. Each plate 24 is provided adj acent its upper edge with a series of alining apertures adapted to be engaged by bolts 25 which are welded or otherwise rigidly secured to the tubes 26, which are slotted along their inner edges, as shown at 26 The projecting ends of the bolts 25 are engaged by nuts 27 by which the relative posi' tions of the opposite tubes 26 may be ad justed in order to regulate the tension of the screen which is connected thereto. A sheet of woven Wire screen cloth 28 extends between the tubes 26 and engages the slots 26* thereof, being wound around longitudinal rods within the tubes or having rods welded there o in order to form an obstruction larger than the slots 26 so that the screen is held in position by the snubbing action of the strands of the screen against the edges of the slot. Each longitudinal strand of the screen is thus held securely in position so that it is possible to secure a uniform tension in the screening medium midway between the tubes 26, and directly above the strap 21, by which the rotary vibrator is secured in position, the screening medium 28 is rigidly secured to the frame 10-by means of a pair of'clamping plates which are secured to the upwardly extending arms 18 of the frame at their ends and clamped to the screening medium at intermediate points by means of bolts31.

The vibrator casing 20 contains a rotary vibrator mechanism of the form described in my previous-applications, and it comprises a longitudinal shaft which extends substantially throughout the length of the casing, being mounted in bearings 36 and raceways 41 secured within the shell. These balls are located on one side only of the shaft, so that as the vibratory members 39 rotate, an unbalanced rotary thrust is imparted to the vibrator casing and trans mitted therefrom through the plates 24 to the screen 28. Since the vibrator casing is held in rigid position at its middle point, it will be apparent that an independent series of vibratlons is set u by each free end of the Vibrator casing. f the slots 39 and the balls 40 carried by the members 39 in opposite ends of the casing are located in the same plane and on the same side of the shaft, the vibrations set up in opposite ends of the casing willbe in phase with each other, but 30 I have found that the results are improved if the balls 20 are located in the same plane but on opposite sides of the shaft, so that vibrations set up in opposite ends of the easing are opposite in phase to those set up in the other end of the casing. It will be obvious that various degrees of phase displacement may be secured by varying the'relative angular positions of the slots 39 in the members 39 located in opposite ends of the casing.

The material to be screened is supplied from a storage chamber located above the upper ed of the screen and arranged to feed the feeding roll 46 which discharges the material onto an intermediate shelf 47, from which itis thrown onto the upper edge of the screen. The crushed material falls by gravity downwardly over the screening medium, and the coarse material which does not pass through the meshes of the screen is discharged over the lower edge thereof into the recelvmg chamber 48. Asthe mat'erial' passes over the screening medium,'it is subjected to one or more series of high frequency circular vibrations imparted thereto by the unbalanced rotary devices within the casing 20. Thus each unit of the woven wire screen moves in a minute circular path which imparts the maximum degree of vibration and agitation to the materials passing downwardly over the screen surface, The operation of the screening apparatus is improved particularly with screens of relatively fine weight and mesh by maintaining in the nely crushed material to a rotary other rhomboidal section 31.

screening medium a high degree of tension through the operation of the bolts 25 and nuts 27. The substantially circular path, through which each particle of the screening medium passes during each cycle of its vibration, comprises two elements of movement which are substantially transverse to the plane of the screen and two elements of movement which are substantially parallel to or within the plane of the screen. This is shown diagrammatically in Fig. 5, where the Woven wire screen is shown on an enlarged scale and a section taken therethrough in a vertical plane which lies transverse to the axis of the vibrator. Each section 28 of one of the wires of the screen moves substantially in a circular path in response to the action of the rotary vibrator, and this circular ath is represented diagrammatically by t e line 30. In the upper part30 of its path, the particle moves substantially parallel to the plane of the screening medium and toward the upper edge thereof, while in the lower part 30 of its path the section of the screen moves downwardly and substantially parallel to the plane of the screen. The other portions 30 and ,30 of the path of the section 28- are substantially normal to the plane of the screen. Since the central portion of the screening medium is held in rigid position with respect to the fixed frame 10, it will be apparent that the vibration of the op osite end portions of the screen 28 will istort the meshes of the screen, so that if these meshes are originally rectangular in shape, for example, they will be' distorted by the vibrations in the plane of the screen into a rhomboidal shape, first in one direction and then in the other. The distortion of the screening medium is represented diagrammatically in Fig. 6 of the drawings where a portion of the screen is shown in an enlarged plan view. The wires 28 of the screen normally form a rectangle, but due tort-he action of the vibrator and to the fact that the screen is held rigidly at its centerfthe'mesh is first distorted in one direction 'to form a rhomboidal section, as shown at 31, and itis then distorted in the other direction to form an- This distortion of 'thefmeshes z-of the screen accomplishes a squeezing action upon the particles condition even after continued use.- The movements of the screening medium, in

planes transverse to the plane of the screen and parallel. to the path of travel of the particles over the screen surface, serve to agitate the particles toa maximum degree and -to effect an efficient screening thereof. In practice, it has been found that under tions are out of phase.

assume some circumstances the eficiency of the apparatus is adected more or less by the direction of rotation of the vibrator. In general, it is found that the etiiciency of the screening apparatus is improved by rotating the vibrator in a direction so that the peripheries of the rotary members move toward the upper edge of the screen in the upper parts of their paths of travel. This movement sets u a corresponding direction of travel of care particle of the screening medium, so that in the upper part of its path each particle of the screen moves .toward the upper ed e or? the screening medium, while throug the lower part of its path of travel each particle of the screening medium moves'toward the lower edge of the screen. This movement of each particle of the screening medium in the upper part of its path of vibration opposes the downward movement of the partic tends to project them upwardly toward the upper edge of the screening surface, thereby tending to delay the passage of the particles over the screening medium and securing greater activity in the movements of the particles and greater efficiency in the screening thereof. It has thus far been found that the effect of the direction of rotation of the vibrator is more marked when the vibrations in opposite ends of the vibrator are in phase with each other than it is when these vibra- Although I have shown and described one embodiment of the invention for purposes of illustration, it will be understood that it may be constructed in various other forms vithout departing from the scope of the appended claims.

I claim:

1. In combination, a vibrator, supporting members carried by said vibrator arranged to be actuated in diiierent phases, and a screen mounted on said supporting members.

2. In combination, a vibrator, a screen cloth, a fixed frame connected to a portion of said cloth adapted to be stationary,

' and means for connecting said vibrator to a free edge of said screen cloth.

3. In combination, a vibrator casing, supporting members connected to said vibrator 5 casing, a screen connected to and mounted between said supporting members, said casing having means therein for producing high frequency vibrations of difi'erent phases in said supporting members.

4b. In combination, a vibrator casing, means for supporting the central part of said vibrator casing, means for producing high frequency circular vibrations in the free end of said casing, supporting members connected tothe end portions of said casing, and a screen cloth connected to and es being screened and oi saidcasing, and means :porting the middle portion of said screen.

extending between said supporting members.

5. In combination, a vibrator casing, means" for supporting said vibrator casing between its ends, supporting members carried by the 7 screen stretched between said supporting, members, and meansv for producing high frequency vibrations inthe end portions of said casing.

6. In combination, a vibrator casing, means connected to the central part of said casing for supporting the same, supporting members connected to the ends of said casend portions of said casing, a

ing, a screen cloth, means connected to said supporting members for maintaining said screen cloth under high tension, and means fit) for producing high freuency vibrations in the end portions of sai casing.

7. In combination a vibrator casin till screen cloth under high tension, and means for producing high frequency circular vibrations in the free ends of said casing, the vibrations in one end of said casing being out of phase with the vibrations in the other end of said casing.

9. In combination, a vibrator casing,

means connected to the central part of said casing for supporting the same,

supporting members connected to the ends of said casing, a woven wire screen cloth, means connected to said supportin members for maintaining said screen c oth under high tension, means for producing high frequency circular vibrations in the free ends for rigidly sup- 10. In combination, a supporting frame,

a vibrator casing having its central portion secured to said frame, supporting members secured to the free ends of said casing, a woven wire screen stretched between said supporting members, means extending across the middle portion of said screen for rigidly securing the same to said frame, and means for producing high frequency circular vibrations in the free ends of said casing.

11. The combination in a screening machine ot a rotary vibrator, means for supbrate, means for producing minute circular Vibrations of high frequency in the end portions of said casing, transmitting plates connected to the end portions ofsaid casing, and a screen cloth extending between and supported by said transmitting plates.

13. The combination in a screening machine of a vibrator casing, means for supporting said vibrator casing at its center leaving the end portions thereof free to vi- -brate, means for producing minute circular vibrations of high frequency in the end portions of said caslng, transmltting lates connected to the end portions of sai casing, a screen cloth extending between said transmitting plates, and means for connecting said screen cloth to said plates and producing tension therein.

14,. In combination, a supporting frame, a vibrator casing having its central part mounted rigidly on said frame, means for roducing minute circular vibrations in the ree ends of said casing in planes perpendicular to its longitudinal axis, transmitting members secured to the end ortions of said casing and extending upwar therefrom, a screen frame secured to "sai members in an inclined position, and a screen cloth mounted on said screen frame.

15. In a screening machine, the combination with a vibrator having a casing, and means to vibrate opposite ends of the casing in paths forming closed orbits.

1-6. In a screening machine,'the combination'with a vibrator centrally mounted and having a casing with projecting ends adapted to execute harmonic motion in planes transverse to the central axis of said ends, of supporting means carried by said ends and a screen on said supporting means.

17. In a screeningmachine, the combination with a vibrator having a casing, and means to vibrate opposite ends of the casing in paths forming closed orbits displaced in phase.

18. In a screening machine, the combination with a vibrator having a casing centrally mounted and provided with projecting tubular ends adapted to be internally actuated to execute harmonic motion in planes perpendicular to the central axis of said ends, of supporting means on said ends, and a screen on said supporting means.

In testimony whereof, I have subscribed my name.

transmitting 

